Several Open issues in C# 4.0

There are a few limitations and things that might work differently than you would expect.

· The DLR allows objects to be created from objects that represent classes. However, the current implementation of C# doesn’t have syntax to support this.

· Dynamic lookup will not be able to find extension methods. Whether extension methods apply or not depends on the static context of the call (i.e. which using clauses occur), and this context information is not currently kept as part of the payload.

· Anonymous functions (i.e. lambda expressions) cannot appear as arguments to a dynamic method call. The compiler cannot bind (i.e. “understand”) an anonymous function without knowing what type it is converted to.

One consequence of these limitations is that you cannot easily use LINQ queries over dynamic objects:

dynamic collection = …;

var result = collection.Select(e => e + 5);

If the Select method is an extension method, dynamic lookup will not find it. Even if it is an instance method, the above does not compile, because a lambda expression cannot be passed as an argument to a dynamic operation.

There are no plans to address these limitations in C# 4.0.